subject: chemistry level: higher...the kinetic model of matter q: what is matter? matter is anything...
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The Institute of Education79-85 Lower Leeson Street, Dublin 2, IrelandTel: +353 1 661 3511Email: [email protected]
CHEMISTRY
HIGHER
ENDA DOWD
The Kinetic Model of Matter
Q: What is matter?
Matter is anything that occupies space and has mass
(Matter is composed of particles (atoms/molecules))
Q: What are the three states of matter?
1) Solids
2) Liquids
3) Gases
Q: What are the properties of the three states of matter?
Note: Liquids and gases, where the particles can move, are known as fluids
Solids Liquid Gas
- Cannot flow - Can flow - Can flow
- Have a fixed shape - Will flow into and take up shape of their container
- Will flow into and take up shape of their container
- Have a fixed volume - Have a fixed volume - Volume expands to fill container
- Cannot be compressed - Cannot be compressed - Can be compressed
- Particles vibrate but attractions/bonds hold them in a fixed position
- Small average distance between particles
- Particles vibrate more vigorously, attractions break, and reform and particles can move past each other
- Greater average distance between the particles
- Particles spaced out, almost all attractions are broken
- Particles move at high speeds in straight lines, colliding randomly with each other and their container
- Greatest average distance between the particles
Q: What is the movement of particles in a fluid, due to random collisions known as?
Brownian motion
Q: How can the Brownian motion be shown?
Q: Explain how tiny air molecules can affect the movement of a much larger smoke particle
The air molecules are moving at such high speeds, they have a very large momentum
Remember: momentum =
- Set up the apparatus in the diagram, with smoke placed
in a glass cell
- Observe the behaviour of the “particles” of smoke
Result:
- The smoke moves and randomly changes direction
Q: Why does this occur?
- The smoke particle is being moved by the air particles
that are moving and randomly colliding with it
Q: The particles in solids, liquids and gases vibrate as they energy. What is the name of this
energy?
Internal energy – relates to the kinetic energy of the particles
Note: The more kinetic energy the particles have, the hotter the material is i.e. the higher its
temperature
Q: What is temperature?
Temperature is the measure of the hotness of an object
Q: What is meant by “hotness”?
Hotness refers to the average kinetic energy per particle in the object
Unit of temperature: a) degrees Celsius (°C) - practical temperature scale
b) Kelvin (K) - SI unit
Degrees Celsius (°C) Kelvin
Q: How is temperature measured?
Using a thermometer
Q: How do thermometers work?
All thermometers monitor a physical property that changes as temperature changes
Degrees Celsius scale:
Kelvin scale:
+ 273.15
- 273.15
Examples of thermometers
(1) Liquid in glass thermometer
Physical property measured: Length of liquid in a tube
- Liquids expand when heated and contract when cooled
- If the liquid is placed in a thin tube the length of the column of liquid will increase as
the temperature increases
- The length can be interpreted to measure temperature
Example: Mercury or Alcohol in glass thermometer
(2) Thermistor thermometer
Physical property measured: Resistance
- The resistance of a thermistor will decrease as temperature increases
- The resistance can be interpreted to measure temperature
(3) Thermocouple thermometer
Physical property measured: Voltage
Q: Give two advantages of using a thermocouple instead of a liquid in glass thermometer
1) A thermocouple has a wider temperature range than a mercury in glass thermometer
2) Thermocouples are more sensitive and respond to changes in temperature more quickly
- A thermocouple consists of two different metals joined to form a
complete circuit
- If the two junctions are placed at different temperatures a voltage
appears in the circuit
- The voltage can be interpreted to measure temperature
Looking at the liquid in glass thermometer
Q: How is a scale calibrated on a thermometer to allow it to measure temperature
Q: What properties of a liquid make it suitable for use in a liquid in glass thermometer?
`1) Sensitivity - The liquid must be sensitive to and expand quickly when the temperature change
Note: Mercury is not as sensitive as alcohol; therefore, the tube used in a mercury thermometer is
more narrow
2) Range – The liquid should have a low freezing point and a high boiling point, so it remains liquid in
the thermometer for a wide range of temperature
3) Linearity - The liquid must expand uniformly as temperature rises or will not be accurate
1. Place an ungraduated mercury thermometer in melting
ice - mark the level of the liquid, lo, on the
thermometer (0°C) – the lower fixed point
2. Place the same ungraduated mercury thermometer in
boiling water – mark the level of the liquid, l100, on the
thermometer (100°C) – the upper fixed point
3. The distance between 0OC and 100OC is divided into
100 equal divisions to allow it to measure each degree
4. Place the same ungraduated mercury thermometer in
water from the tap – mark the level of the liquid, lx, on
the thermometer
Result: The temperature of water from the tap water
can be found using the graph shown
r
Heating solids, liquids and gases
Q: What happens to solids, liquids and gases when they are heated and cooled?
Solids, liquids and gases expand when heated and contract when cooled
The expanding of solids, liquids and gases when heated is known as thermal expansion
Q: Why does thermal expansion occur?
Looking at a solid
Note:
Solids expand slightly when heated as the particles can vibrate but cannot move their position due
to the strong attractions between them
Liquids expand more than solids as the particles vibrate more and the particles move further away
from each other as the attractions between them can be broken
Gases expand most of all as the particles vibrate more and the particles move furthest away from
each other as there are very little attractions between them
Showing solids expand when heated and contract when cooled
“bar breaker experiment”
- When the particles are heated, they
acquire more kinetic/internal energy
- They vibrate more, move a greater
distance and take up more space
- The solid, as a whole, expands
Heat
- Heat the steel bar as shown and tighten the screw
on the bar simultaneously
- The steel bar will expand
- Allow the steel bar to cool
Result: The contraction of the steel bar will cause the cast
iron peg to snap as the pressure acting on it becomes too
great.
Showing liquids expand when heated and contract when cooled
Showing gases expand when heated and contract when cooled
Q: Give two applications of matter expanding when heated and contracting when cooled
- Set up the apparatus in the diagram marking the level of water
in the glass tube
- Heat the flask
Result: The level of water in the tube rises as the liquid expands#
- Cool the flask
Result: The level of the water in the tube drops as the liquid contracts
- Set up the apparatus in the diagram
- Heat the air in the flask
Result: Bubbles of air are pushed out through the glass tube into
the water as the gas expands
- Cool the flask
Result: Water in sucked back up the glass tube and into the flask
as the gas contracts.
1) Bimetallic thermostat – strip made of two
different metals
Expand and contract to turn heating in a room on
and off
2) Liquid in glass thermometers - Contain mercury
or alcohol that expand when heated and
contract when cooled allowing the temperature
to be read
Q: Give an undesirable consequence of matter expanding when heated and contacting when
cooled
Looking at pressure in gases
The particles in gases move randomly at high speeds
They collide with each other and with the walls of their container
As they collide with another particle or a wall there is a change in momentum
Remember: momentum =
The force on the particles =
And the pressure on each particle =
- Train tracks can warp and buckle in hot weather
Note: Gaps are now left in train tracks to prevent this
occurring
Gaps left
Q: How does changing the volume on the gas’ container affect the pressure on the gas?
Relationship between pressure of a gas and volume - If the temperature is kept constant, the
pressure is inversely proportional to the volume
In other words – Double the volume, the pressure halves
Halve the volume, the pressure doubles
Explaining why
- The volume decreases
- The number of collisions between the gas particles increases, as they have less volume
- The pressure increases
Q: How does changing the temperature of a gas affect the pressure on the gas?
Relationship between pressure of a gas and temperature - If the volume is kept constant, the
pressure is directly proportional to the temperature
In other words – Double the temperature, the pressure doubles
Halve the volume, the pressure halves
Explaining why
- The temperature increases
- The kinetic energy and speed of the gas particles increases
- The change in momentum of each collision is greater, meaning the force of each
collision is greater
- The pressure increases